One of commuters' worst nightmares occurred on a train in New Jersey during Monday evening's rush hour.

A passenger aboard a NJ Transit commuter train from New York's Penn Station fell to the tracks after the train's conductor opened its doors on the wrong side, where there was no platform.

The agency conformed the incident, which went viral on Twitter, to Business Insider. Gothamist reported that the man only suffered minor injuries and declined further medical care.

"NJ TRANSIT launched an immediate investigation into the incident," a representative said. "Preliminarily, the cause appears to be human error, but the investigation remains ongoing."

Garden State commuters aboard the North Jersey Coast Line train told NBC News that they had to run through three train cars to tell a conductor about the incident, who was unaware a man had fallen to the tracks, while other riders pulled the emergency brake.

Door incidents, while rare, highlight just how important the warnings to avoid leaning on the doors of any train can be. New York City's subway system employs black and white signs, and requires conductors point at them when arriving at every station, to avoid an incident like Monday's.

The little-known workflow, which occurs every single time a train stops at the system's 472 stations, inspired a 2013 viral video that caught conductors' responses to funny handmade signs held below the zebra markings.

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